Switching DC-to-DC converters having a multi-phase coupled inductor topology are described in U.S. Pat. No. 6,362,986 to Schultz et al., the disclosure of which is incorporated herein by reference. These converters have advantages, including reduced ripple current in the inductors and the switches, which enables reduced per-phase inductance and/or reduced switching frequency over converters having conventional multi-phase DC-to-DC converter topologies. As a result, DC-to-DC converters with magnetically coupled inductors achieve a superior transient response without an efficiency penalty compared with conventional multiphase topologies. This allows a significant reduction in output capacitance resulting in smaller, lower cost solutions.
As known in the art, coupled inductor windings must be inversely magnetically coupled to benefit from a coupled inductor in a multi-phase DC-to-DC converter design. Inverse magnetic coupling in a two-phase DC-to-DC converter can be appreciated with reference to FIG. 1, which shows a schematic of a two-phase DC-to-DC converter 100. DC-to-DC converter 100 includes a coupled inductor 102, which includes two windings 104, 106, and a magnetic core 108 magnetically coupling windings 104, 106. A respective first terminal 110, 112 of each winding 104, 106 electrically couples to a common node 114, and a respective second terminal 116, 118 of each winding 104, 106 electrically couples to a respective switching node 120, 122. In the present disclosure, terminals of a coupled inductor that are electrically coupled to a respective switching node in a DC-to-DC converter application (e.g., terminals 116, 118 in DC-to-DC converter 100 of FIG. 1) will sometimes be referred to as switching terminals of the coupled inductor. Additionally, terminals of a coupled inductor that are electrically coupled to a common node (e.g., terminals 110, 112 in DC-to-DC converter 100 of FIG. 1) will sometimes be referred to as common terminals of the coupled inductor in the present disclosure.
A respective switching circuit 124, 126 is also electrically coupled to each switching node 120, 122. Each switching circuit 124, 126 switches its respective second terminal 116, 118 between at least two different voltage levels. DC-to-DC converter 100 could be configured, for example, as a buck converter, where switching circuits 124, 126 switch their respective second terminal 116, 118 between an input voltage and ground, and common node 114 is an output node. As another example, DC-to-DC converter 100 could be configured as a boost converter, where each switching circuit 124, 126 switches its respective second terminal 116, 118 between an output node and ground, and common node 114 is an input node.
Coupled inductor 102 is configured such at it has inverse magnetic coupling between windings 104, 106. As a result of such inverse magnetic coupling, a current flowing through winding 104 from switching node 120 to common node 114 induces a current in winding 106 flowing from switching node 122 to common node 114. Similarly, a current flowing through winding 106 from switching node 122 to common node 114 induces a current in winding 104 flowing from switching node 120 to common node 114 because of the inverse coupling.
Various coupled inductors have been developed for use in multi-phase DC-to-DC converter applications. For example, FIG. 2 shows a side view of a prior-art two-phase (i.e., two winding) coupled inductor 200. Coupled inductor 200 includes two windings 202 wound through a magnetic core 204. FIG. 3 shows a perspective view of one winding 202 separated from core 204. Although coupled inductor 200's design promotes ease of printed circuit board (PCB) layout and is scalable to more than two-phases, windings 202 are relatively complex, and inductor 200 may therefore be difficult and costly to manufacture. Additionally, windings 202 are relatively long and thus typically have relatively high impedance.
As another example, two-phase coupled inductors with staple style windings have been developed. FIG. 4 shows a perspective view of a prior art two-phase coupled inductor 400, which is representative of such inductors. Coupled inductor 400 includes two staple style windings 402 wound through a magnetic core 404. In contrast to windings 202 of coupled inductor 200, staple style windings 402 are relatively simple, thereby promoting ease of manufacturing and low cost of coupled inductor 400. Additionally, windings 402 have a relatively short length, thereby promoting low DC winding resistance. Therefore, coupled inductor 400 generally has a lower cost and exhibits a lower winding resistance than many other types of prior coupled inductors, such as coupled inductor 200 of FIG. 2.
However, a DC-to-DC converter including coupled inductor 400 must be configured such that one terminal on each side of the inductor is electrically coupled to a respective switching node, to achieve inverse magnetic coupling. Specifically, a DC-to-DC converter including coupled inductor 400 is configured such that one terminal on side 406 is electrically coupled to a respective switching node, and one terminal on side 408 is electrically coupled to a respective switching node, to achieve inverse magnetic coupling. Two terminals on a same side of coupled inductor 400 cannot serve as switching terminals if inverse magnetic coupling is to be realized. Such constraint imposed by coupled inductor 400 is undesirable in many DC-to-DC converter applications, as discussed below.
For example, a DC-to-DC converter including coupled inductor 400 typically must be configured such that the converter's switching circuits are located on different sides of inductor 400. In particular, as known in the art, DC-to-DC converter switching circuits must be located near their respective inductor switching terminals for reliable and efficient DC-to-DC converter operation. For example, in DC-to-DC converter 100 of FIG. 1, switching circuit 124 needs to be located near switching terminal 116, and switching circuit 126 needs to be located near switching terminal 118, for efficient and reliable DC-to-DC converter operation. Thus, in a DC-to-DC converter including coupled inductor 400, inductor switching terminals are on opposite sides of coupled inductor 400 to achieve inverse magnetic coupling, and the DC-to-DC converter switching circuits therefore generally must be located on different (e.g., opposite) sides of coupled inductor 400 to be near their respective inductor switching terminals. It can be undesirable to locate switching circuits on different sides of a coupled inductor as doing so may prohibit use of a common heat sink to cool all switching circuits and/or complicate DC-to-DC converter layout when driving a load accessed from one side of the converter.
As another example, a DC-to-DC converter including coupled inductor 400 may require one or more PCB traces of long, narrow, and/or complex shape to electrically couple terminals of the inductor to other components of the DC-to-DC converter. In particular, if a DC-to-DC converter including coupled inductor 400 is configured such that the inductor switching terminals are on opposite sides of the coupled inductor to achieve inverse magnetic coupling, the DC-to-DC converter necessarily must also be configured such that the inductor common terminals are on opposite sides of the coupled inductor. The fact that the inductor common terminals are on opposite sides of the inductor typically necessitates a relatively long, narrow, and/or complex shaped PCB trace to connect the common terminals to a common node. Narrow or long traces are generally undesirable as they typically have high impedance, which may result in excessive losses and/or unreliable operation. Complex shaped traces (e.g., non-rectangular) may also be undesirable as they may be difficult to manufacture and/or prone to short to other traces.
For example, FIG. 5 shows one prior art PCB layout 500 for use with coupled inductor 400 in a two-phase DC-to-DC converter application. Only the outline of coupled inductor 400 is shown in FIG. 5 to show details for layout 500. Layout 500 includes pads 502, 504, 506, 508 for electrically coupling to terminals of coupled inductor 400. Pads 502, 508, which electrically couple to respective switching nodes, are located on opposite sides 510, 512 of coupled inductor 400 to achieve inverse magnetic coupling. Switching circuits 514, 516 are respectively coupled to pads 502, 508 by conductive PCB traces 518, 520. Switching circuits 514, 516 are also located on opposite sides 510, 512 of coupled inductor 400. Pads 504, 506, which electrically couple to a common node, are also on opposite sides 510, 512 of coupled inductor 400. As a result of pads 504, 506 being on opposite sides of inductor 400 and the location of switching circuits 514, 516, a relatively long and narrow conductive trace 522 is required to connect pads 504, 506 to a common node.
As another example, FIG. 6 shows another prior art PCB layout 600 for use with coupled inductor 400 in a two-phase DC-to-DC converter application. Layout 600 includes pads 602, 604, 606, 608 for electrically coupling to terminals of coupled inductor 400. Pads 602, 608, which electrically couple to a respective switching circuit 610, 612 via a respective conductive trace 614, 616, are located on opposite sides of coupled inductor 400 to achieve inverse magnetic coupling. Pads 604, 606, which, electrically coupled to a common node via a conductive PCB trace 618, are also located on opposite sides of coupled inductor 400. The fact that pads 604, 606 are on opposite sides of coupled inductor 400 and the location of switching circuits 610, 612 requires conductive trace 618 to be relatively long and narrow and to have a complex shape.